This invention relates to a process and an apparatus to produce solid particles from a flow of molten material.
A number of processes are used to produce solid particles from a flow of molten material, which are known as granulating processes generally, granulating processes comprise pouring a flow of a molten material into a granulating chamber, where this downward flow of molten material is atomized by a dispersion member, causing this flow to disperse in a number of particles of molten material.
Said particles of molten material are quenched by contacting a cooling agent, usually water, in order to make a rapid cooling-off of the particles, thus forming the desired granules. A large volume of water is usually used to quench the dispersed particles of molten materials, in a relationship ranging from nine to twenty parts of water for one part of molten material.
Prior granulating processes produce granules of different sizes, which should be separated from the water after quenching, requiring the use of auxiliary separating equipment, therefore increasing costs.
Another problem with known processes of quenching by water is the risk of explosions. It is known that contact between extremely hot molten material particles and water results in violent reactions, which can jeopardize the operators and the facilities.
The quenching of the particles can occur inside of water reservoirs having an explosion-proof shield in order to preclude such risking conditions that might cause safety problems, therefore increasing the costs of the equipment.
In the recent years searches have been made to develop new processes which use fewer volumes of water rendering them safer for the operators and facilities.
U.S. Pat. No. 5,667,147 to Alfred Edlinger is an example of such approaches, which discloses a process and an apparatus for granulating molten materials. A jet of molten material is introduced by means of an injector into a mixing chamber, where a flow of compressed air and water is injected to promote dispersion of said jet of molten material within the chamber. The water injected into the chamber expands, rendering high kinetic energy to the dispersed particles. Particles of solidified material are injected into an area of a reduced cross section, located below the chamber.
After passing through such area of a reduced cross section the dispersed particles pass them through a diffuser, crossing a transverse flow of vapor coming from another diffuser, provoking more dispersion of the particles. Next, the particles impinge against a baffle plate, for attaining the desired size.
The fact of the dispersion of the particles is based on an expansion of water into a closed chamber is a drawback for the use of the apparatus and the process disclosed in U.S. Pat. No. 5,667,147, as it requires an accurate control of the volumes of injected water for the desired expansion to occur, which is not that simple to accomplish. This makes the operation critical and can eventually impair achievement of the goal, that is, the obtainment of solidified granules of molten material.
The apparatus for extracting heat and for solidifying molten material particles object of the present invention comprises at least one ejector of dispersing/cooling agent which provides a flow of a high pressure dispersing/cooling agent which substantially transversely traverses a downward flow of molten material so as to cause a dispersion effect which forms and cools particles of molten or semi-molten material. Said flow of high pressure dispersing/cooling agent comprises water and a high pressure gas.
It can be further provided with at least one low pressure gas duct providing a flow of a low pressure dispersing/cooling agent which substantially transversely traverses said flow of particles of molten or semi-molten material, in order to enhance the dispersion and cooling-off effects.
Said particles of molten or semi-molten material impinge against a transporting device, which transport them to a collecting place. The transporting device is provided with a vibrator, which provides a vibrating movement to the transporting device to prevent the particles which are still cooling-off from being agglomerated again.
The transporting device is also provided with a sloping device, which allows the inclination of the transporting device to be varied, in order to make possible the particles to remain a shorter or longer period on the transporting device so as to give the particles time enough for cooling-off.
A hopper can be further provided, which serves to collect the dispersed particles and to carry them onto the transporting device so as to prevent any particles from being launched outside the transporting device. The hopper is provided with a vibrator, which provides a vibrating movement to the hopper to prevent the particles which are still cooling-off from being agglomerated again.
Cooling water pipes could be provided to eject a flow of cooling water onto the internal walls of the hopper and also onto the transporting device, which assist cooling of the dispersed particles. This water cooling flow serves also to protect the walls of the hopper against heat.
The transporting device could be provided with multiple stages, and an air/water cooling pipe could be provided to eject a substantially transversely air/water cooling flow against the particles falling from a stage of the transporting device onto a following stage.